1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus, which manufactures flat displays of liquid crystal, organic electro-luminescence (EL) and the like by irradiating an object with laser light to change physical property of the object. More specifically, the present invention relates to a semiconductor manufacturing apparatus which as suitable for a flat display manufacturing system irradiating amorphous silicon or polysilicon formed on an insulating board with laser light to change physical property of a silicon film.
2. Description of the Conventional Art
A display apparatus in recent years has used a liquid crystal element as a display element. The liquid crystal element (a pixel element) or a driver circuit of the liquid crystal element is configured with a thin film transistor (hereinafter referred to as TFT). In a manufacturing procedure of the TFT, a step to modify amorphous silicon formed on a glass substrate to polysilicon is required. In this connection, “changing physical property of an object” is called “modification” in the present specification, and the modification includes not only changing amorphous silicon to polysilicon but also changing physical property of a material.
The modification process is to modify a silicon film by laser irradiation. As illustrated in FIG. 10, the modification step includes a process for forming an undercoat film (SiO2) 73 on an insulating substrate 72 of quartz glass or alkali-free glass, where the undercoat film 73 prevents entering of impurities from the insulating substrate 72; a process for forming an amorphous silicon film surface 74 on the undercoat film 73; a process to irradiate the amorphous silicon film surface 74 with a linear laser beam 75 by using a high-output laser as a light source; a process for modifying amorphous silicon to a polysilicon 74B by scanning the linear laser beam 75 in a lateral direction 74A; a process for cutting out polysilicon only at a position in which the TFT is configured; a process for forming an gate oxide film (SiO2) on the cut-out and attaching a gate electrode at an uppermost part; a process for injecting predetermined impurity ions into the oxide film (SiO2) and forming a source/drain; and a process for erecting aluminum electrodes on the source/drain, covering the whole with a protection film, and making the TFT In addition, SiN or SiON can be sandwiched between the insulating substrate 72 and the undercoat film 73.
In the aforementioned modification process of a silicon film by laser irradiation, excimer laser annealing by an excimer laser is generally used. In the excimer laser annealing, a polysilicon film is formed by irradiating a silicon film with a XeCl excimer laser having a wavelength of 307 nm and a pulse width of several-ten nanoseconds, which has high light absorptivity, injecting comparatively low energy of 160 mJ/cm2, and quickly heating up the silicon film to a melting point. The above excimer laser has features that it has a large output of several-hundred watts, can form the large linear laser spot having a larger length than one side of a rectangular mother glass, and can collectively and efficiently modify the whole surface of the silicon film formed on the mother glass. In the modification of silicon by the excimer laser, since the crystal grain size of polysilicon, which strongly affects the performance of the TFT, is as small as 100 nm to 500 nm, an electric field effect mobility which is an index of the TFT performance can be made to be about 150 cm2/V·s.
In recent years, a system-on-glass has been proposed and partially realized, where the system-on-glass includes high performance circuits such as a control circuit, an interface circuit, an arithmetic circuit and the like, in addition to the pixel element on the flat display and the driver circuit. The TFT of the system-on-glass is required to have high performance, and is required to be modified into polysilicon with high quality (having large crystal grains). The patent document 1 listed below describes a technique related to the modification into polysilicon modification with high quality. The patent document 1 discusses that an amorphous silicon film with high quality having large crystal grains long in the scanning direction is formed by using a solid state laser for exciting a semiconductor as a light source, continuously emitting light (CW) from the laser, and scanning a laser beam irradiated on a silicon film. Furthermore, the patent document 1 discusses that a high performance TFT having an electric field effect mobility of 300 cm2/V·s or more is formed by previously patterning amorphous silicon in a ribbon shape or an island shape at a position where the high performance TFT is required.
In the excimer laser annealing and the solid-state laser annealing, it is desired that power density of the laser spot irradiated and formed on the silicon film surface is comparatively high and spatial laser strength distribution is uniform. One reason why these are desired is that, in the modification procedure including crystals of the silicon film, it is necessary to inject energy capable of performing the modification in a short time (several-ten ns to several-ten μs) before heat is transferred to a laminated film adjacent to the silicon film. In addition, another reason is to avoid spatial strength unevenness of the laser strength distribution, which affects modification spots directly.
The patent document 2 listed below discusses a technique of a method for shaping a strength distribution of an excimer laser light. According to a beam homogenizer (an optical module for equalizing a profile of laser light on an irradiation surface) described in the patent document 2, a lens group consisting of a cylindrical lens, a fly-eye lens, and the like is arranged at a later stage of excimer laser output, and a desired spot shape and laser strength distribution on the silicon film surface are finally obtained.
Furthermore, the patent document 3 listed below discusses a technique for condensing laser light output from a plurality of low output solid-state lasers at one position by optical fibers, and irradiating a silicon film with the condensed laser light through an optical waveguide unit. The patent document 3 discusses that laser light irradiated from a plurality of laser light-emitting elements is condensed by using an optical fiber body, and the condensed laser light is branched and irradiated into a plurality of branch passages by using the optical waveguide unit.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-86505    Patent Document 2: Japanese Patent Application Laid-Open No. H9-129573    Patent Document 3: Japanese Patent Application Laid-Open No. 2007-88050